The present invention pertains to a blade tensioner for applying tension to a chain, and in particular to a blade tensioner having a blade shoe with a chain sliding face, a plate-like blade spring for applying spring force to the blade shoe, and a base for supporting the blade shoe at one end while allowing it to pivot freely.
A blade tensioner is often used to apply tension to a chain. A conventional tensioner may be configured primarily with a blade shoe having a chain sliding face, a base which allows the base part of a blade shoe to pivot freely and its tip part to slide freely, and several plate-like blade springs stacked on the side opposite the chain sliding face of the blade shoe in order to apply spring force to the blade shoe.
During the operation of the chain, the chain may advance while sliding on the chain sliding face of the blade shoe. At this time, a load generated by the deformation of the blade shoe and the blade springs is applied to the chain, so that constant tension of the chain can be maintained. In addition, vibrations due to slippage of the chain and/or fluctuations in tension are propagated to the respective blade springs in the blade shoe via the blade shoe. At this time, when the respective blade springs are subjected to repeated elastic deformation, a damping force can be created by means of adjoining blade springs sliding against each other, in order to damp the vibrations of the chain.
Incidentally, the conventional blade tensioner is used, e.g., for an oil-pump drive chain, at a position where the inter-axial distance in the engine is relatively short. On the other hand, due to the demand for low cost engines, the use of a blade tensioner which can be produced relatively inexpensively by means of a simple structure for a cam chain driven between the crank shaft and the cam shaft is also in demand.
However, if an attempt is made to apply an unmodified blade tensioner to a long chain, such as a cam chain, with a long inter-axial distance, the total length of the blade shoe and the blade spring may have to be increased, the natural frequency of the blade tensioner can drop, and the resonance frequency of the blade tensioner can decrease. As a result, the blade tensioner may resonate within the duty cycle range of the engine, which may result in fatigue breakdown.
Thus, a blade tensioner capable of preventing fatigue breakdown by preventing such resonance in the duty cycle range of the engine has been suggested by the present applicant, such as disclosed in Japanese Patent Application No. Hei 11[1999]-207816.
In the aforementioned blade tensioner, the position where the blade spring or the blade shoe contacts the base is at the midpoint of the blade shoe; whereby, frequency of the blade tensioner can be set relatively high. As a result, resonance of the blade tensioner in the duty cycle range of the engine can be prevented, so that fatigue breakdown due to resonance can be prevented.
On the other hand, for recent applications of blade tensioners, there is great demand for a blade tensioner capable of applying even greater damping forces to the chain. However, this need may not be satisfied sufficiently by the aforementioned blade tensioner.
The blade tensioner according to an aspect of the invention comprises a blade shoe having a sliding face on which the chain slides; a base supporting the aforementioned blade shoe at one end while allowing it to pivot freely; and a plate-like blade spring that is fixed at one end to one of the ends of the aforementioned blade shoe, that contacts the side opposite the aforementioned chain sliding face of the aforementioned blade shoe at the other end, and that contacts the aforementioned base within its curved middle section in order to apply spring force to the aforementioned blade shoe.
In a blade tensioner according to an aspect of the invention, when vibrations due to slippage of the chain and/or fluctuations in tension are applied to the blade shoe, not only may sliding resistance be generated as the curved part at the midpoint of the blade spring slides against the base, but sliding resistance may also be generated as the other end of the blade spring slides against the side of the blade shoe opposite the chain sliding face, so that the damping force of the blade tensioner can be further improved by this sliding resistance.
In this case, a friction material may be provided at the other end of the blade spring or the side of the blade shoe opposite the chain sliding face. Alternatively, a friction material may be provided at the curved part of the blade spring or the contact face between the curved part of the blade spring and the base. When this kind of friction material is provided, a blade tensioner with increased damping force can be realized.
Although the friction material can be provided by means of bonding, welding, or coating, it may also be injection-molded. Furthermore, the friction material may consist of rubber, plastic, or friction paper.
Preferably, the blade shoe has a cross section with a U-like shape. This allows the rigidity of the blade shoe to be improved, so that vibrations of the chain can be controlled more easily.
In another aspect of the blade tensioner, a friction material is provided at the aforementioned other end of the aforementioned blade shoe.
In another aspect of the blade tensioner, the aforementioned friction part is attached to the aforementioned other end of the aforementioned blade spring by means of bonding, welding, or coating.
In another aspect of the blade tensioner, a friction material which contacts the aforementioned other end of the aforementioned blade spring is provided on the reverse face of the aforementioned chain sliding face of the aforementioned blade shoe.
In another aspect of the blade tensioner, the aforementioned friction material is attached to the side opposite the aforementioned chain sliding face of the aforementioned blade shoe by means of bonding, welding, or coating.
In another aspect of the blade tensioner, the aforementioned friction material is injection-molded onto the side opposite the aforementioned chain sliding face of the aforementioned blade shoe.
In another aspect of the blade tensioner, a friction material is provided at the contact face between the aforementioned curved part of the aforementioned blade spring and the aforementioned base.
In another aspect of the blade tensioner, the aforementioned friction material is attached to the aforementioned curved part of the aforementioned blade spring by means of bonding, welding, or coating.
In another aspect of the blade tensioner, a friction material is provided at the contact face between the aforementioned base and the aforementioned curved part of the aforementioned blade spring.
In another aspect of the blade tensioner, the aforementioned friction material is attached to the aforementioned base by means of bonding, welding, or coating.
In another aspect of the blade tensioner, the aforementioned friction material may comprise rubber, plastic, or friction paper.